AbstractWe present the results of tomographic inversion computed with the use of the LOTOS code for Sicily and surroundings, a region of great geodynamic interest located on the Nubia-Europe margin where previous analyses have progressively improved the knowledge of seismic velocity structure without, however, permitting fine detection of tectonic units and structural discontinuities. We used LOTOS's devices for inversion, grid rotation and adaptation to ray density for application to a dataset of 7105 local earthquakes of the period 1990-2012. Our tomographic model highlights a previously undocumented major discontinuity which is located approximately along the northern coast of Sicily and is characterized by a sudden transition from low velocity imbricate thrust sheets and accretionary wedge in mainland Sicily (to the south) to relatively high velocity Tyrrhenian continental crust (to the north). Combining this finding with available geological and geodynamic information, we conclude that this northern Sicily seismic velocity discontinuity, which approximately corresponds to a regional fault system known as Kumeta-Alcantara, may have played a major role in the Miocene to Middle Pliocene, when lithosphere tearing occurred between the Tyrrhenian sea and Sicily in response to trench retreat. The more recent geodynamic settings of northern Sicily and the southern Tyrrhenian can be unravelled from Quaternary geological observations, seismicity and GPS data, which indicate that (i) the northern Sicily discontinuity has ceased to be active in more recent times; and (ii) the reorganized slow convergence of Nubia with respect to Europe is currently accommodated ~100 km north of Sicily, along the east-trending seismogenic belt enclosing Ustica and the Aeolian Islands.

AbstractWe performed a new analysis of updated and accurate sets of seismic and GNSS data relative to the southern Tyrrhenian region. Detailed velocity field and crustal strain distribution coming from integration of episodic and continuous measurements at more than 160 geodetic sites (spanning the 1994-2015 period) have been evaluated together with the spatial distribution of recent seismicity and an updated catalogue of waveform inversion fault-plane solutions relative to the period 1976-2014. In agreement with previous investigations, we have found that the kinematics of the study area is quite homogeneous except for the north-eastern corner of Sicily which moves almost coherently with southern Calabria in response to the SE-ward rollback of the Ionian slab. The rest of the study region shows a NNW-trending velocity field in agreement with the direction of the Nubia-Eurasia convergence and it is mainly interested by a major compressive domain. NNW-oriented compression is particularly highlighted by seismic data along the E-W trending seismic belt located in the southern Tyrrhenian Sea. In the framework of such compressive regime, the E-W trending extensional domain of northern Sicily is also clearly depicted both by seismic and geodetic data. The cause of this extensional domain framed inside a mainly compressive one represents an open question in the recent scientific debate. Comparisons between our results and literature information on regional geology and crustal structure led us to investigate whether the extension could occur as local response to the thrusting dynamics of the southern Tyrrhenian belt, favoured by the presence of pre-existing weakness zones. We then propose a first attempt to evaluate such a possible causal relationship by means of Finite Element Method (FEM) and Coulomb Stress Change (CSC) modelling. In particular, we adopted a FEM approach to investigate the deformation pattern produced by thrust faulting of southern Tyrrhenian belt, along a 2D profile crossing both the compressive belt and the extensional one in northern Sicily. We also estimated the CSC due to the thrust faulting on normal receiving faults fairly reproducing pre-existing structures of northern Sicily. Modelling results indicate that the thrust faulting activity along the Southern Tyrrhenian compressive margin could be effective in promoting extensional processes in northern Sicily. We have so shown that the local response to thrust faulting activity may concur, even in combination with other processes, to generate the crustal stretching of northern Sicily.